The present invention relates to a feeding apparatus for creation of one or more plugs of compressible material for feeding into a gasifier or reactor, wherein the apparatus comprises a piston feeder with at least three pistons for pre-compressing and delivering compressible material towards a mouthpiece serving as a non-return valve and having an exit end facing a braking device with friction means for regulating the final degree of compression of the material, and an opposing inlet end for inlet of at least partly compressed material.
An apparatus of this type is, for example, used in connection with combustion of alternative fuels such as residual products like hay, wood chip, scrap paper and other material, which otherwise will be seen as waste materials. These types of materials are often of uneven structure and un-pure, which puts up high requirements for the equipment used for processing them. An example is hay, which can contain impurities such as sticks and even small animals as mice. This of course demands equipment with a large flexibility and with wide operating parameters when it comes to for example, structure, density, hardness and elasticity of the processed materials. This flexibility is even more important as the same equipment is often used to handle different types of materials.
A feeding apparatus of the present type has been disclosed in the applicants own International patent application no. WO 93/23709. While this feeding apparatus solves several problems of the at the time existing feeding apparatuses, which typically use different types of screw feeders for grinding and feeding, it still had some severe drawbacks. These drawbacks are evident when the feeding apparatuses of WO 93/23709 is used in situations where dense plugs are needed and in situations where the pressure difference across the formed plugs are high, as it will be in relation with many modern reactors. The hourglass shape of the mouthpiece in WO 93/23709 allows for only a relatively loose compression of the material as else the pressed plug cannot pass through the narrow part of the mouthpiece. This result in loosely pressed plugs but still with a high risk of blockage of the mouthpiece as is the case in most other feeders within this field of technology. Such blockages are unwanted, as they requires full stop of the machinery in order to be taken care of.
Thus there still exist a need for a feeding apparatus providing a safe, efficient and reliable way for feeding materials into for example a gasifier or reactor.